Liang-Quan Sheng

Determination of nitrofuran metabolites in shrimp by high performance liquid chromatography with fluorescence detection and liquid chromatography-tandem mass spectrometry using a new derivatization reagent.

A high performance liquid chromatography with fluorescence detection (HPLC-FLD) method for the simultaneous determination of total nitrofuran metabolite residues (furazolidone, furaltadone, nitrofurantoin, and nitrofurazone) in shrimp was developed. The method involves the acid hydrolysis of protein-bound metabolites, followed by the derivatization of the freed metabolites with the new fluorescent derivatization reagent 2-hydroxy-1-naphthaldehyde (HN) and subsequent liquid-liquid extraction (LLE). Separation is achieved on a YMC-Pack Polymer C18 column under alkaline conditions, and the high fluorescence intensity of the derivatives at an emission wavelength Em=463nm (Ex=395nm) enables, for the first time, their simultaneous determination in shrimp at concentrations as low as 1μg/kg by HPLC-FLD. The method was validated using blank shrimp fortified with all four metabolites at 0.5, 1.0 and 2.0μg/kg. Recoveries were >87% with relative standard deviations of <8.1% for all four metabolites. Furthermore, the results obtained by HPLC-FLD were in very good agreement with those obtained by LC-MS/MS analysis.

Cadmium(II) and zinc(II) complexes with rigid 1-(1H-imidazol-4-yl)-3-(4H-tetrazol-5-yl)benzene and varied carboxylate ligands

Six new coordination polymers [Cd2(HL)2(pbda)(H2O)2]·4H2O (1), [Cd2(HL)2(mbda)(H2O)2]·6H2O (2), [Cd(H2L)(mmbda)(H2O)] (3), [Cd2(H2L)2(btca) (H2O)2]·4H2O (4), [Zn2(H2L)2(btca)] (5) and [Zn6(H2L)6(btca)3] (6) were synthesized by reactions of cadmium(II)/zinc(II) salts with a rigid ligand 1-(1H-imidazol-4-yl)-3-(4H-tetrazol-5-yl)benzene (H2L) and different carboxylic acids of 1,4-benzenedicarboxylic acid (H2pbda), 1,3-benzenedicarboxylic acid (H2mbda), 5-methyl-1,3-benzenedicarboxylic acid (H2mmbda), 1,2,4,5-benzenetetracarboxylic acid (H4btca), respectively. The structures of the complexes were determined by single crystal X-ray diffraction analysis. Although complexes 1 and 2 possess the same two-dimensional (2D) network with (4·82)-fes topology built from Cd(II)–(HL)− moieties, different coordinated orientation of auxiliary carboxylates of pbda2− and mbda2− pillar the 2D layer into distinct frameworks. Complex 1 is an unusual binodal (3,4)-connected three-dimensional (3D) dmc net with Point (Schlafli) symbol of (4·82)(4·85) while 2 is a rare binodal (3,4)-connected 3D architecture with a (4·6·8)(4·62·83) fsc-3,4-C2/c topology. Complexes 3 and 4 have the same 2D networks with (4,4) topology, and H-bonding or π–π stacking interactions extending the 2D layers into 3D supramolecular frameworks, respectively. Complexes 5 and 6 present a pair of pseudopolymorphs, and 5 is an uninodal (4,4)-connected 3D net with Point (Schlafli) symbol of (62·84)(64·82)2 while 6 is an unprecedented penta-nodal 4-connected net with (4·62·83)2(4·64·8)2(62·84)(64·82)4 topology. The thermal stability and photoluminescent property of the complexes were investigated.

A novel “turn-on” fluorescent probe for Fe3+ in aqueous media based on CN isomerization

A new type of fluorescent probe (L) for Fe3+ based on CN isomerization was synthesized. It shows fluorescence enhancement (turn-on) response for Fe3+ in aqueous media (v(CH3CN):v(H2O) = 1:9). The complexation mode and the corresponding fluorescent enhancement mechanism were elucidated by IR spectra, transient spectra, Job plot, and DFT calculations.

Kinetics and mechanism of jack bean urease inhibition by Hg2

BackgroundJack bean urease (EC 3.5.1.5) is a metalloenzyme, which catalyzes the hydrolysis of urea to produce ammonia and carbon dioxide. The heavy metal ions are common inhibitors to control the rate of the enzymatic urea hydrolysis, which take the Hg2+ as the representative. Hg2+ affects the enzyme activity causing loss of the biological function of the enzyme, which threatens the survival of many microorganism and plants. However, inhibitory kinetics of urease by the low concentration Hg2+ has not been explored fully. In this study, the inhibitory effect of the low concentration Hg2+ on jack bean urease was investigated in order to elucidate the mechanism of Hg2+ inhibition.ResultsAccording to the kinetic parameters for the enzyme obtained from Lineweaver–Burk plot, it is shown that the Km is equal to 4.6±0.3 mM and Vm is equal to 29.8±1.7 μmol NH3/min mg. The results show that the inhibition of jack bean urease by Hg2+ at low concentration is a reversible reaction. Equilibrium constants have been determined for Hg2+ binding with the enzyme or the enzyme-substrate complexes (Ki =0.012 μM). The results show that the Hg2+ is a noncompetitive inhibitor. In addition, the kinetics of enzyme inhibition by the low concentration Hg2+ has been studied using the kinetic method of the substrate reaction. The results suggest that the enzyme first reversibly and quickly binds Hg2+ and then undergoes a slow reversible course to inactivation. Furthermore, the rate constant of the forward reactions (k+0) is much larger than the rate constant of the reverse reactions (k-0). By combining with the fact that the enzyme activity is almost completely lost at high concentration, the enzyme is completely inactivated when the Hg2+ concentration is high enough.ConclusionsThese results suggest that Hg2+ has great impacts on the urease activity and the established inhibition kinetics model is suitable.

Solvent-dependent “turn-on” fluorescence chemosensor for Mg2+ based on combination of CN isomerization and inhibition of ESIPT mechanisms

A fluorescent chemosensor (L) for Mg(2+) has been synthesized and characterized, which exhibits turn-on fluorescence response for Mg(2+) only in alcohol solvent (methanol or ethanol) with high sensitivity and selectivity. But in both nonpolar and polar solvents (cyclohexane, DCM, DMSO or MeCN), L showed negligible fluorescent response for Mg(2+). In order to discover the unique phenomenon, optical measurements, liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and a high performance liquid chromatography with a fluorescence detector (HPLC-FLD) of L and L with Mg(2+) ions in solvents were studied. In alcohol solvent, [L+alcohol molecule] was formed and the mechanism aspect of L concerning the remarkable fluorescence response for Mg(2+) has been discussed.

A highly selective colorimetric and fluorescent chemosensor for Al(III) based-on simple naphthol in aqueous solution.

A colorimetric and fluorescent chemosensor (L) for Al(III) was synthesized and fully characterized. L could be both used as a colorimetric and fluorescent chemosensor for the detection of Al(3+) ions with low detection limit (8.87×10(-7) M) in CH3CN-H2O (1:1, v/v) solution. The binding ratio of L-Al(3+) was determined from the Job plot (absorption and fluorescence spectra) and MALDI-TOF MS data to be 1:1. The binding constant (Ka) of Al(3+) binding to L was calculated to be 4.8×10(5) M(-1) from a Benesi-Hildebrand plot. Moreover, the binding site of L with Al(3+) was determined by (1)H NMR titration experiment.

High-performance liquid chromatography with fluorescence detection for the determination of nitrofuran metabolites in pork muscle

A simple and sensitive HPLC method with fluorescence detection (HPLC-FLD) is reported for the simultaneous determination of metabolites of four nitrofuran drugs (furazolidone, furaltadone, nitrofurantoin and nitrofurazone) in pork muscle. The method involves acid hydrolysis of the protein-bound drug metabolites and the conjugation of the released side-chains with a novel fluorescence agent 2-hydroxy-1-naphthaldehyde. After liquid–liquid extraction and effective separation of the derivatives on a YMC-Pack Polymer C18 column at 40°C under alkaline conditions, the high fluorescence intensity of these derivatives at emission wavelength λem = 463 nm enables their simultaneous determination in pork muscle at concentrations as low as 1 µg kg−1. The method was validated using blank pork muscle fortified with all four metabolites at 0.5, 1.0 and 2.0 µg kg−1. Recoveries were > 92.3% with RSDs < 8.5% for all four metabolites. The results obtained with HPLC-FLD and LC-MS/MS methods showed very good agreement for pork muscle samples. Graphical Abstract

(E)-2-Hydroxy­naphthalene-1-carb­al­de­hyde semicarbazone

The title compound, C12H11N3O2, adopts an E or trans configuration with respect to the C=N bond. There is an intramolecular O—H⋯N hydrogen bond involving the hydroxyl H atom and an N atom of the hydrazine group. In the crystal structure, molecules are connected via N—H⋯O hydrogen bonds, forming a three-dimensional network.

Mechanism, kinetics, and antimicrobial activities of 2-hydroxy-1-naphthaldehyde semicarbazone as a new Jack bean urease inhibitor

A new inhibitor of jack bean urease, 2-hydroxy-1-naphthaldehyde semicarbazone (HNDSC), was synthesized and its inhibitory mechanism and kinetics with respect to jack bean urease were investigated. HNDSC inhibited the activity of jack bean urease, with the inhibitor concentration leading to 50% activity loss (IC50) of 0.032 ± 0.004 mM. Kinetic analyses showed that HNDSC is a reversible and competitive inhibitor of jack bean urease. Microscopic rate constants were obtained by the progress-of-substrate-reaction method. The results obtained from inhibitory kinetic and fluorescence titration assay methods showed very good agreement that one molecule of HNDSC binds the active unit of the jack bean urease. The inhibition mechanism and kinetic studies indicate that HNDSC could be a candidate for the development of new urease inhibitors. Its antibacterial activities, evaluated against Escherichia coli, Bacillus subtilis, and Staphyloccocus aureus, were highest against E. coli.

(E)-1-[(2-Hy­droxy-1-naphth­yl)methyl­idene­amino]­imidazolidine-2,4-dione

The title compound, C14H11N3O3, adopts an E or trans configuration with respect to the C=N bond. In the molecule there is an intramolecular O—H⋯N hydrogen bond involving the hydroxy substituent at the 2-positon of the naphthalene ring and the adjacent methyleneamino N atom. The molecule is roughly planar, the dihedral angle between the naphthalene and imidazolidine-2,4-dione mean planes being 8.4 (1)°. In the crystal, pairs of N—H⋯O hydrogen bonds link molecules into inversion dimers. These dimers are futher linked via C—H⋯O interactions, forming a three-dimensional network.